Measuring Gene Expression

iGEM Davidson – Missouri Western 2010:Foundational Advances in Biology and the Knapsack Problem

The Davidson/Missouri Western multidisciplinary team is using synthetic biology to address a mathematical problem in Escherichia coli. Specifically, we are addressing the Knapsack Problem, an NP-complete problem that asks, “Given a finite number of weighted items, can one find a subset of these items that completely fills a knapsack of fixed capacity?”

In our design, weighted items are represented by versions of TetA genes that confer measurably distinct levels of tetracycline resistance. We have altered the codons of the wild type TetA gene, optimizing and de-optimizing several segments of the coding sequence. Each TetA variant is coupled with a distinctive fluorescent gene, and each pair of genes is flanked by lox sites. In the presence of Cre protein, the lox mechanism either inverts or excises the coding sequence, yielding different combinations of expressed TetA variants. An expressed variant corresponds to an item being placed in the knapsack. Over-expression of TetA results in cell death, which represents exceeding the capacity of the knapsack. Under-expression of TetA causes the cells to stop growing due to tetracycline in the growth medium, which represents not completely filling the knapsack. Surviving cells correspond to cells within a certain range of TetA production and the fluorescence tag allows for comparative measurement within this range.

The team is also working to develop software tools relevant to the specific project and applicable to projects in the wider synthetic biology community.

Team

The 2010 iGEM team from Davidson College and Missouri Western State University is composed of multidisciplinary undergraduate students. The team includes math, biology, computer science, and chemistry majors. View the Davidson-Missouri Westernteampage.

Project

In an attempt to solve the knapsack problem, we explored a variety of different topics. We optimized the codons for a portion of the TetA gene in order to produce variant genes that confer differing amounts of tetracycline resistance. We also created 11 variant lox sites that have differing recombination frequencies. Finally, we explored gene expression of RFP and the TetA gene. View the work done by Davidson and Missouri Western undergrads.